Conventionally, power consumption decreasing techniques for electric watches are established, and small primary batteries are used as power sources of the electric watches. The primary batteries are, however, disposable, and replacement of batteries is troublesome, and it is estimated that terrestrial environmental pollution due to the disposal of the primary batteries becomes more serious problem in the future. In view of such problems, power generating type electric watches, which use secondary batteries charged with power generating energy instead of the primary batteries, are put into practice. The power generating energy is obtained from energy sources such as solar power generation using solar battery, thermoelectric power generation using a temperature difference between an atmosphere and a wrist, and mechanical power generation using a revolution cone.
The power generating type electric watches, therefore, are eco-friendly, but the energy to be built up is not enough, and thus there arises a potential problem that the lack of the charged energy with which the secondary batteries are charged deteriorates reliability of time holding. Particularly in mechanical analog wrist watches, in order to reduce the consumption of the energy as much as possible, a wheel train mechanism is driven by a minimum driving torque. For this reason, when a shape of hands is large, there is a fear that time indication by the hands is shifted due to shock, disturbance, and the like, and in order to prevent this, the shape and size of the hands have a certain limitation.
Further, in a calendar display mechanism of mechanical electric watches for displaying time using mechanical hands, date of a date display section should be corrected manually at the end of the month approximately every two months. For this reason, it is very troublesome and difficult to use the mechanical electric watches. When a complicated mechanism is adopted, a month-end automatic correcting function can be added, but since such a function has a complicated mechanism, the assembly cost becomes high, and the reliability of a stable operation for a long time is deteriorated. Since the power consumption increases, it is difficult to operate in an uninterruptible manner with the charging energy. When only a date section adopts electro-optical liquid crystal display in order to solve this problem, a time display surface provides improper design.
In order to eliminate the above disadvantage, a function for detecting a mechanical angle and a rotating position of hands display and calendar display is necessary. Conventionally suggested techniques are as follows. (1) Japanese Patent Application Laid-Open No. 57-67877 discloses a technique that a mechanical switch is provided to a portion of a rotational wheel train. (2) Japanese Patent Application Laid-Open No. 8-179058 discloses a technique that a light emitting element and a light receiving element are arranged so as to sandwich a rotational wheel train having a hole and the light receiving element detects presence/non-presence of the hole at the time of rotation. (3) Japanese Patent Application National Publication No. 2001-524206 or (4) U.S. Pat. No. 6,307,814 discloses capacity detection in which electronic detecting means detects a change or the like in electric properties including capacity change between electrodes utilizing a rotating member.
Publicly known references relating to the present invention include: (5) Japanese Patent Application Laid-Open No. 54-91278 which discloses a position detecting system which is provided with a mechanically contact switch on a part of a rotational wheel train; (6) Japanese Patent Application Laid-Open No. 2000-35489 which discloses a system where a light emitting element and a light receiving element are arranged so as to sandwich a rotational wheel train having a hole and a light receiving optical switch detects presence/non-presence of the hole at the time of rotation; and (7) Japanese Patent Application Laid-Open No. 54-92360 which discloses a position detecting mechanism adopting capacity detection for detecting a change in a capacity between hands, a wheel train or the like and a position detecting member due to a rotating movement.
The position detecting mechanisms which have been suggested, however, have a lot of disadvantages. The position detection (1) which utilizes the mechanical contact switch mechanism has a constitution where a position is detected by contacting with the rotating movement member such as the wheel train, and thus requires many driving energy. This disadvantage becomes a serious problem particularly for the power generating type electric watches having insufficient power generating energy, and the position detection might cause a shift of the position. Further, the contact switch mechanism causes abrasion of the contact member, and thus reliability is low.
In the constitution (2) utilizing an optical sensor, since it is necessary to arrange the light emitting element and the light receiving element on upper and lower surfaces of a rotating member, a thickness of the watch increases. For this reason, this constitution cannot be adopted to thin wrist watches. Considerable electric power consumption is required to operate optical elements such as the light emitting element and the light receiving element, and thus the detection is carried out only about once a day. Since driving voltage having a threshold value higher than a certain value is necessary for light emission, it is difficult to apply this constitution to power generating electric watches having large fluctuation in a power supply voltage.
In the constitution (3) or (4) where a change in the capacity between the electrodes is directly detected by the rotating member, since a change in the capacity which is detected by a very small position detecting part adaptable to a size of wrist watches is very small, detecting accuracy is low. Further, the detection is easily influenced by external environment such as changes in position, temperature and the like due to carrying postures, and thus the reliability of the position detection is very low.
It is an object of the present invention to provide an electric watch having a position detecting system with high reliability for being capable of securely detecting a time difference between mechanical holding time and electric holding time. The position detecting system of the present invention solves the above problems, does not require a lot of energy, avoids a problem caused by a defective contact or the like due to aged deterioration of a contact type detecting mechanism so as to prevent deterioration of reliability, realizes a constitution thinner than an optical sensor system, does not require a high voltage for driving a light emitting element, and is not influenced by external environment such as temperature as compared with a system for detecting a change in an electrostatic capacity and in an absolute quantity of a magnetic force.